This invention relates to particulate material for forming molds, particularly those which are suitable for producing precision castings, and a method for producing such particulate material.
In one type of method for forming molds known in the art, water is added in suitable amount to ethyl silicate to form a solution, to which particulate refractory material and a gelation promoting agent are added to prepare a refractory slurry. The slurry is charged around a pattern of soluble material to form a mold. After gelation, the mold is immersed in water to completely harden the mold and at the same time to allow the pattern to melt out of the mold. Finally, the mold is dried and fired.
When components of particulate material differ from one another in specific gravity, refractory particles of high specific gravity will sink in a mass of slurry, with a result that the completed mold will have different charging rates at different portions. In such case, the strength and dimensional accuracy of the mold will be adversely affected.
When a mold is assembled, machining is necessary in some cases. When this is the case, the use of refractory particles of coarse grain size will cause a reduction in surface precision of the mold due to the coarse grains appearing on the surface of the mold.